Tokyo: Tokyo is seeking an explanation from Washington on the alleged US spying on the Japanese government and companies, the media reported on Monday.
"We are strongly asking US director of national intelligence to check the facts," chief cabinet secretary Yoshihide Suga said over the US national security agency's alleged interception.
"If the alleged spying were true, Japan would find it extremely regrettable," Xinhua news agency cited Japan's Kyodo News Agency as saying.
The Wikileaks website on Friday posted NSA reports and a list of 35 Japanese targets for telephone intercepts, including the Japanese cabinet office, the Bank of Japan, the country's finance and trade ministries, and major Japanese trading companies.
The eavesdropping dated back to prime minister Shinzo Abe's first government in 2006, and one report from telephone intercepts of senior Japanese officials could have been shared with Australia, Canada, Britain and New Zealand - the US intelligence partners.
Asked about Japan's security measures for secret information, the top government spokesman said, "I believe such secrets will never be leaked because the government is taking all possible measures to prevent leaks."